The merger of two neutron stars, one year on: GW170817

Can it really have been a year since GW170817, and the subsequent detection of electromagnetic radiation from its source? Read this very nice piece by my erstwhile Cardiff colleague Bernard Schutz, who gives an insider’s view of the story.

One of the things I remember about this was the fascinating way in which various `outsiders’ used a comments thread on this blog to piece together the clues to what going on!

The Rumbling Universe

Last Friday we celebrated the one-year anniversary of an event that those of us who were involved will never forget. The Virgo gravitational-wave detector had joined the two LIGO instruments on August 1, 2017, and the three detectors had since then been patiently listening out together for gravitational wave sounds coming from anywhere in the Universe. On August 17, the deep quiet was interrupted by a squeal, a chirp lasting much longer and going to a much higher pitch than the GW150914 chirp that had launched the field of gravitational wave observational astronomy two years earlier. We named it, prosaically, GW170817.

GW170817-rendition [Credit: NSF/LIGO/Sonoma State University/A. Simonnet] This one-minute-long squeal was followed by an incredible explosion that radiated intense gamma-rays, X-rays, light, radio waves — right across the whole electromagnetic spectrum. What came first was a burst of gamma-rays, just 2 seconds after the end of the squeal. Then…

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3 Responses to “The merger of two neutron stars, one year on: GW170817”

  1. “Can it really have been a year since GW170817, and the subsequent detection of electromagnetic radiation from its source?”

    Tempus fugit as they said in Rome, not that long ago. Yes, indeed. Seems like yesterday. And almost 100 years since the famous eclipse expeditions.

  2. Only a year ago, too few questions were asked while many, many issues were raised.

    Copious inconsistencies and deficient shortcuts LIGO employed to overcome its magnetometer issues and an incapacity to produce an effective algorithm that accurately estimates the false alarm probability (FAP) should, despite the appearance of truth, give us warning that we may be conflating events and/or detecting something other than pure non-dispersive and classical gravitational waves.

    Click to access 1601.00130.pdf

    “The relative uncertainty in the estimation is larger when the FAP is smaller. The relative uncertainty reaches 100% when the FAP is about 10^−4 , for the experiment parameters chosen in this MDC. This value depends on the expected number of coincident events and the number of single detector triggers.”

    Coincident geophysical-space physical response to magnetospheric mode recorded in ACE, GOES, and cloud-ground lightning discharge data surrounding GW events – open notes made publicly-available prior to publication:


    The issue with correlated LIGO magnetic noise has been known for almost two decades, and LIGO has continued to publish articles discussing terrestrial magnetic noise as a persisting limiting factor for detection of a stochastic GW background. Issues with magnetometer placement and shortcomings are discussed as a rule in such papers. Globally-coherent magnetic noise has been found in cross-correlation between magnetometer data captured in Poland and North America

    Lags between observer-dependent group arrival and the scaling and morphology of putative sources for GW are also readily identified as those produced by the inter-detector line-of-sight thunderstorms absent in literature; others writing on the topic have somehow ignored these storms, or the notion of discharge signal superposition and extended high energy glows now known from thunderstorms, or that global pulsations are not rare and are the exception to arguments against Schumann resonance-linked waveguide enhancement of transverse magnetic modes.

    There exist excess correlations between LIGO event parameters and multiscaled-periodic physical systems that remain unexplained.

    LIGO magnetometer Z-component time evolution of local magnetic field is ignored due to problems with instrument channel saturation at moving intervals <5 min.

    Placement choice for magnetometers must consider the cumulative field feedback enhancement generated between magnetometers, which obscures signal symmetry (their own and as an addition to background EM with thermal noise) and can saturate signals. This is usually presented conservatively, as only a challenge to gravitational wave astronomy from the stochastic gravitational wave background, with filtering schemes to remove correlated noise signals for residual/null signal analysis Calibration to data-quality signal sensitivity lock between both detectors during science runs is achieved no more than 60% of total LIGO runs, not considering Virgo (as only two detectors are required to identify a high-likelihood LIGO GW transient candidate). Simple joint probability for maximum quality coverage for data completion during dual active science run phases with full calibration lock hovers around 0.2.

    Mind you I am suggesting that the Creswell et. al correlated lags are from real geomagnetic signals and that echoes of black hole merger signals reported by several teams of authors in cross-spectral density are merely artifacts of these coincident quasiperiodic coupling intervals during magnetospheric sawtooth events. They may be induced by GW propagation into plasma-magnetic field structures at critical stages, but is this the most parsimonious explanation?

    In response to Creswell et al. 2017, Green and Moffat have found that residual correlations between detector-specific strain phase can be eliminated without utilizing matched templates, demonstrating that improper choice of templates is not the source of imperfect template subtraction. This is accomplished by assuming smooth signals and ideal bandwidths and performing wavelet transforms – hardly an unbiased approach. Realize that correlated noise, having the same time lags as arriving LIGO transients, becomes significant many minutes prior to and following the peaks of these transients without any application or subtraction of template (as LIGO GW signals are extracted from a band-passed and whitened signal with prior mean noise component amplitude a magnitude above strongest GW peak strain). So, template matching error may or may or may not be an artifact that necessitates LIGO parameter revision (hopefully, refinement) for source signal properties, but the correlated strain noise that surrounds the detections will not go away, and foreground effects are a viable possibility in this light. Possible future revisions to LIGO source values are expected to constrain LIGO objects within the cutoffs for conventionally-detected x-ray black holes, not provide evidence against the detection of GW from cosmic objects per se.

    From Magnetism and Advanced LIGO (Daniel and Schofield, October 6, 2014)

    “LIGO plans to monitor magnetic fields because they can affect the interferometer’s signals. A magnetic field from a Schumann Resonance can affect both LIGO interferometers in a similar way as a gravitational wave. Magnetic field data can be used to figure out whether a signal was caused by a gravitational wave or a magnetic field. We evaluated the quality of four remote locations that can be used to measure Schumann Resonances and Ultra Low Frequency (ULF) waves. Furthermore, eleven magnetometer set-ups around the LIGO Hanford Observatory (LHO) will allow for monitoring magnetic fields specific to LHO. All eleven magnetometer set-ups were improved. Filter boxes were modified in order to obtain accurate magnetic field measurements at 10 Hz. Finally, I determined how close the Uninterruptible Power Supply (UPS), an electronic device that produces a large magnetic field, can be to the interferometer.
    [… . …]
    When starting to calibrate one of the magnetometers in the LVEA, DTT’s time series plot was saturated. The maximum number of counts provided by the ADC was consistently exceeded. In other words, all the data was not fitting on the DTT time series plot, so calibrating in this state would produce an incorrect calibration factor. The power spectrum showed a tall peak at 60 Hz. The surrounding, fluctuating magnetic fields from the 60 Hz wires which power the entire LVEA, especially the clean rooms, were so strong that magnetometer’s sensitive measurements could not be accurately viewed on DTT. To calibrate the magnetometers, one must wait until the clean rooms are gone.”

    The claim of being "unbiased" requires that exhaustive, redundant, and eclectic mathematical analysis is practiced and scrutinized by a third party at every stage of a research program with equal treatment to all data sources – environmental as well as experiment-generated – preceding establishment of the properties of an object. It is difficult not to have noted the array of wildly-divergent models suggested/supported/invited at this point by those working with LIGO data. Considering this phenomenological chaos and given strong LIGO opposition to particular theoretical camps, a new analysis of the LIGO data with appreciation of the total possible power of a higher-order phenomenon and an openness to unforeseen and serendipitous physics may be productive. Even if it may be completely surprising and difficult to accept that initial LIGO experimental design and statistical modeling are imperfect, it may be easy to reject their phenomenological conventions ( black hole echoes, interpretations of GW170817 remnant and x-ray curve, possible GW150914 GRB).

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